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Tuesday, May 31, 2011

Noise levels in a Saab convertible

Recently I've found an older article called "Top-down cruising can damage your hearing" repeated several times over the Internet. It's about a study measuring noise levels in convertibles with a warning and conclusion stating that "sounds over 85 decibels can be damaging" in long-term or repeating exposure.

So I was curious about noise levels in my Saab 9-3 convertible and wanted to measure it at least a bit properly. I've never felt that I am at the edge of a hearing issue, that the noise level is annoying or  damaging. Am I partially deaf already ? Maybe. I'd like to find out.

Since my HTC Desire microphone peaks at 83 decibels and than switches off (or what), I've asked a friend with iPhone 4 to go with me on a ride and measure a bit. iPhone 4 peaks at 105 decibels. For this objective it is enough as interesting are levels 85+ decibels. For measurement we used Soundmeter from Faberacoustical, which seems to be serious in their work.

We drove this way (76km) trying to be as realistic as possible and measure different environments - a normal city road, 4 lane city road (2+2), bridge, tunnel, highway and land road. Radio on at normal level, we spoke a bit etc. Windows were up.

Here are the results, I am posting them in order as they've been measured :

1) City 1 and city 2 :

This is a combination of a two lane road and a four lane road in a city outside of traffic peaks. Speed 50-60kmh (31-37 mph). In average the magical 85 decibels were not reached. The peaks came from trucks around and a stupid Skoda Superb driver with at least 90kmh in 60kmh traffic. Another peak was reached at a Apollo bridge over Danube river, which is a four lane road but not highway.

2) Highway bridge in a city + highway tunnel :

This is a bit different story. There were (un)fortunately no trucks on the bridge (max 90kmh / 56 mph), than the average would be definitely higher. In a tunnel the sounds are echoing from everywhere and it's really loud. Max speed in the tunnel was 80kmh (50 mph). But both the bridge as well as the tunnel are not long-term and mostly not repeating. It was this bridge (Harbour bridge) and this tunnel (Sitina tunnel).

3) Highway

This is a clean warning. Don't drive on a highway with roof down. But who does it ? Cabrio drivers mind the highway in general and if they must, they close the roof. With exception like car brand or tuning sessions etc. This is measured at 140kmh  (87 mph). In 160 kmh (100 mph) it was + 5 decibels, which is far above the "safe range" of 85 decibels.

4) Land road

These levels are measured at normal land road between villages at ~90kmh (56mph). Average, normal traffic. The two peaks at the left picture were motorbikes in the opposite direction. This is not very quiet but still somehow ok. I did several long trips (200km+) without any problem.

The sound level also depends  on road surface. Panel roads are loud. Every hole in the road which you dont avoid makes a decibel peak. The holes on inroads on bridges are making high peaks (10-15 decibels).

The original article is saying "even one long trip could result in temporary hearing loss, a phenomenon also noted by those who spend long hours at loud concerts". Well loud concertes go well above 100 decibels. That can cause whistle in the ears, I experienced that in the past. But I had never an issue in a convertible.

140 dB Space rocket at blastoff
130 dB Jackhammer
120 dB Ambulance siren, Amplified rock band, Thunder clap
115 dB Sandblasting
110 dB Woodworking shop
100 dB Pneumatic drill, Chainsaw
90 dB Lawn mower, Disco dance music, Shop tools, Truck traffic, Noisy restaurant
80 dB City traffic, Loud music from radio
75 dB Kitchen appliances
70 dB Crowded restaurant
65 dB Conversation speech
60 dB Sewing machine, Typewriter
50 dB Average home interior
40 dB Quiet residential community
30 dB Whisper at five feet
20 dB Leaves rustling in a breeze
10 dB Normal breathing
0 dB Faintest sound heard by a human ear
Source: (with interesting articles)

Conclusion : 
If someone is aware of a probability of a hear problem, he/she behaves accordingly. It is to recommend to avoid high speeds with the top down, avoiding highways and driving more in a cruising mode than speeding. Actually this is the intention of a convertible - to enjoy the ambient in a chilly cruising way. To have the horse power when it's needed, that's a different story. But this story happens mostly with the top down.

Thanks Eva for the ride, the measurements and the screenshots.

Enjoy the summer :)


  1. good research.. interested to know the noise level under the same condition with the top up. wonder if it'll go over the magic 83 db.

    1. :) ok it's summer starting now, reason to make another test. But. I'm driving often a Volvo with D5 engine. Without any measurements, the noise level of the Saab with top up and of the Volvo are the same. The only thing the convertible makes is a bit higher noises at roof parts above the rear window at higher speeds. But when the opportunity comes, I will measure it .)